In an existing cellular system, an array of base station antennas is generally arranged horizontally. A beam of a base station transmitter can only be adjusted horizontally, but may be inclined vertically at a fixed angle for each User Equipment (UE), so various beam-forming/pre-coding and other technologies are generally applicable to horizontal channels. Since a radio signal is propagated in the three-dimension space, and the performance of the system may not be made optimum due to the fixed downward inclination angle, it is of great significance for the performance of the system to be improved by adjusting the beam vertically. As the radio technologies are developing, such an array of active antennas has emerged in the industry that each array element can be controlled separately. This array of antennas makes it possible to dynamically adjust the beam vertically.
There is such an existing solution to three-dimension beam-forming that a base station deploys a plurality of Channel State Information-Reference Signal (CSI-RS) resources in the horizontal dimension, and the base station applies different vertical beam-forming vectors to the respective CSI-RS resources for beam-forming, and transmits CSI-RS signals over the respective CSI-RS resources. A user equipment measures each CSI-RS signal set in the horizontal dimension, and reports Channel State Information (CSI), and the base station determines three-dimension beam pre-coding information based upon the feedback of the user equipment.
With the solution above, there may be both a significant resource overhead of the system, and high complexity of the user equipment.